The term industrial waste is generally understood to refer specifically to the liquid waste produced as a result of some industrial operation, as distinct from an industry's solid refuse or its gases, fumes and vapors. Like municipal sanitary sewage, most of such liquids must ultimately be disposed of into rivers or other water courses. The liquid wastes of a community, with domestic sewage or industrial wastes, should receive appropriate treatment before discharge into streams in order to prevent gross pollution. The treatment methods for domestic sewage are based on a fundamental and growing body of knowledge. These methods, however, are not suitable for all industrial wastes, which are quite varied in character. Frequently, a new industrial process will produce a waste that is not amenable to treatment by any of the then existing conventional methods. For such new wastes, laboratory investigations followed by pilot-plant studies must precede final design of a method of treatment and the materials thereby utilized.
A number of chemicals will combine with water or the constituents present therein to produce flock, a gelatinous precipitate which aids considerably in clarification of the water during sedimentation. During formation and settling of the flock many of the finely divided particles, including microorganisms, are collected and some of the dissolved substances, particularly those that impart color, are absorbed. The use of flocculating agents is believed to have been originally intended as a pretreatment before utilization of rapid sand filters. However, the good results obtained have led to their use in sedimentation procedures which will not be followed by filtration. Of the various chemicals that can be used for this purpose, aluminum sulfate, commonly called "alum" is employed quite extensively. Ferric salts are conventionally accepted substitutes, especially if the pH of the water is not suitable for alum flocculation. These trivalent cations are very effective in precipitating negative colloids. Both aluminum and iron form gelatinous percipitates in slightly alkaline solutions and the extent to which these added salts participate in the precipitation depends, to a large extent, upon the pH of the water. Since the amount of precipitate and the efficiency of removal of suspended matter by these conventional materials are dependent upon a favorable pH it is often possible to improve the effectiveness of the alum treatment by a prior adjustment of pH. In most cases such adjustments are necessary when there is insufficient alkalinity.
The amount of alum required for proper clarification and color removal is dependant upon the character of the water, the methods of handling, and length of sedimentation to be used. The amount needed in any given situation has to be determined by experimentation.
Unfortunately, it is known that the sludge or flock created by conventionally used salts such as (a) ferric chloride [FeCl.sub.3 ], (b) ferric sulfate [Fe.sub.2 (SO.sub.4).sub.3 or Fe.sub.2 (SO.sub.4).9H.sub.2 O], (c) aluminum sulfate (alum) [Al.sub.2 (SO.sub.4).sub.3 or Al.sub.2 (SO.sub.4).sub.3.18H.sub.2 O], (d) aluminum chloride [AlCl.sub.3 ], (e) sodium aluminate [Na.sub.2 Al.sub.2 O.sub.4 or NaAlO.sub.2 ] or (f) ferrochlorosulfate [ClSO.sub.4 Fe] possess substantial swelling properties and retain large amounts of water. This retention of water has considerable adverse economic impact on the water purification process and any process which further includes the incineration of the sludge or flock created therefrom since materials retaining large amounts of water will be more difficult to remove from solution by filtration and are not readily incinerated. Moreover these conventional flocculants do not perform well in combination with other chemical treatments of waste water since their efficiency is effected by the pH of the water, the chemical composition of the water (including other treatment additives) and the water temperature.
Another problem which is associated with many of the presently used conventional water purification flocculating materials and, in particular, the basic metal salts of aluminum chloride or aluminum sulfate is that these materials are not entirely stable and tend to produce hydroxide precipitate which has drastically reduced coagulating or flocculating properties. Additionally, the manufacture of these conventional materials is somewhat complicated and difficult to carry out on a large scale industrial basis. For example, production of basic aluminum chloride or basic aluminum sulfate generally requires long reaction times (10 to 18 hours) sophisticated chemical systems which may be uneconomical, filtration and/or neutralization operations. Yet another problem associated with most of the basic aluminum salts is that they cannot be readily diluted because such action would result in hydrolytic reactions which tend to deactivate the flocculating properties of the product through formation of hydroxide precipitate. Various attempts to improve the stability and coagulation properties of these basic aluminum compounds through utilization of new technologies have been undertaken. One such improvement is by incorporating iron into the structure of the basic molecule. The technology involved is quite sophisticated and requires special equipment and involves long reaction times (from 50 to 150 hours) under pressure. This technology presently appears to have more theoretical meaning than practical utility.
Another attempt in improving the stability and flocculating properties of basic aluminum sulfate has been directed to reacting aluminum sulfate with phosphoric acid. This procedure has strong drawbacks in that the presence of phosphorus in the chemical structure of the material could have a negative impact on the environment and the quality of water in which the material is used. An even further problem which has been associated with these conventional flocculating agents is that they are not very stable in time and generally hydrolyze to their metal hydroxide precipitates which, usually, are no longer active as coagulating agents.
While aluminum has no redox or sulfide chemistry comparable to iron, its amphoterism and solubility impose definite limitations on aluminum sulfate usage. In particular, the solubility of the predominant equilibrium species when aluminum sulfate is utilized, Al(OH).sub.4.sup.-, is greatly dependent upon pH. In more acidic solutions, having pHs of less than 3, the equilibrium concentration of this ionic species is lower. Accordingly, the optimal pH range for utilization of aluminum sulfate is from about 5.5 to about 6.5.
A problem associated with the production of conventional aluminum chloride, in the form of aluminumhydroxychloride, is that commercial production of this material is only accomplished under difficult processing conditions. For example, those processes presently known involve reaction times of between about 15 and 22 hours and utilization of aluminum oxide particles having specific sizes. Furthermore the reaction temperature of about 105.degree. C. must be followed by the steps of filtration, concentration and passage of material through a IR-45 amberlite anion exchange resin.
Another known flocculating material which is available on a commercial scale is believed to be produced in Japan and marketed under the tradename "TAKI-PACS". This material is believed to be a polyaluminumchloride sulfate flocculating material. The material is believed to have the following general composition: EQU [Al.sub.18 (OH).sub.21 (Cl).sub.27 (SO.sub.4).sub.3 ]
This product is believed to be made in accordance with the following chemical reaction: EQU 11 AlCl.sub.3 +Al.sub.2 (SO.sub.4).sub.3 +5NaAlO.sub.2 +NaOH+10H.sub.2 O.fwdarw.Al.sub.18 (OH).sub.21 (Cl).sub.27 (SO.sub.4).sub.3 +6NaCl
The sodium chloride is believed to be a stabilizer. Unfortunately, this product is not stable in time and is easily hydrolyzed to aluminum hydroxide and its associated salt. The resulting materials have extremely reduced or no flocculating properties.
In order to accomplish efficient destabilization (flocculation) of waste water colloidal suspensions while utilizing salts of iron or aluminum one must recognize that the properties of these flocculating materials are highly dependent upon zeta potential-pH relationships and ongoing hydrolytic reations. For example, since the isoelectric point of ferric hydroxide generally coincides with the general region of minimum stability of colloidal waste water solutions, its utilization generally yields a hydrolyzed primary flocculant having a desireable zeta potential. Unfortunately, in many situations, it is difficult to make use of this desirable situation because of the presence of sulfides or other strongly reducing agents in the solution to be treated. The presence of these materials causes reduction of the ferric ion to the ferrous ion and formation of mixture iron sulfides which generally do not have satisfactory flocculation properties. As a matter of fact these materials may contribute to stabilizing the colloidal suspension rather than destabilizing it. In response to this problem the new flocculating adducts of the present invention shift the zeta potential and the zeta potential-pH relationship to a region where the iron material is a good coagulant. A further advantage of the flocculating adducts of the present invention is that the aluminum and/or iron are not in the hydrate form. The hydrate form carries a negative charge which adversely affects water treatment processes because, as is generally known, waste water colloids are generally negatively charged.
The materials in the present invention were developed in response to the need for improved flocculating materials having greater stability, improved dilution capabilities and an ability to work satisfactorily in a wide range of pHs. Accordingly, I have found that the magnesium or calcium flocculating adducts of the present invention, when made in a highly concentrated form by way of a semi-solid state reaction, have a high trapped cationic charge which may be generally expressed as Me.sup.3+ .fwdarw.Me.sup.2+ .fwdarw.Me(OH).sup.+. This form decreases dissociation of aluminum or iron particles carrying a high positive charge as opposed to the hydrate form carrying a negative charge.
The compounds of the present invention cause rapid flocculation and also reinforce the formation of aggregates of particles which generally results in the tightening or bonding together of the particles and an increased rate of flocculation and settling. The supernatant formed therefrom is less turbid and quite clear. Additionally, less sludge is produced. As was stated above, the products of the present invention are more stable than presently known conventional products which have a tendency to hydrolyze and form hydroxide precipitate and associated salts. The presence of magnesium in the flocculating agents of the present invention is believed to be responsible for their increased stability and resultant increased shelf life.